Device and method for guiding a continuous web by means of a pivotable apparatus

ABSTRACT

In a method or device for guiding an endless web, the endless web is guided via a first positionable roll to an additional positionable roll with a predetermined angle of wrap on each roll, shafts of the rolls lying parallel to one another in a plane and being held by a frame. The web is fed to and led away from the positionable rolls via a respective first stationary roll and a respective additional stationary roll. The frame is pivoted relative to the stationary rolls about a first axis of rotation substantially perpendicular to the plane in order to modify a position of an edge of the web in a direction of the positionable roll shafts. The frame is pivoted relative to the stationary rolls about a second axis of rotation one component of which runs parallel to a movement direction of the web between the positionable rolls.

BACKGROUND

The present preferred embodiment relates to devices for guiding anendless web as used for example in a printer or copier. The presentpreferred embodiment also relates to methods for guiding an endless web.

In the guiding of a paper web through a printer, non-uniform mechanicalproperties of the web or a basic setting of the various guide rolls thatis not precisely parallel can result in a lateral shifting of the paperweb, and can cause the formation of waves in some areas and/or saggingat one side of the web, even if the front edge is running in a stablefashion. At points of deflection with counter-pressure or back pressurerolls, as are, for example, required for transport, such waves can bepressed to form folds. In addition, sagging at one side of the web, forexample in the area of a fixing station that operates in contactlessfashion, is disturbing, because the sagging web segment can come intocontact with mechanical parts, so that the toner images are smudged, orthe sagging segment is exposed to an excessively high energy load.

From U.S. Pat. No. 5,021,673, a device is known for guiding a paper webin which for the guiding of the web, rolls are situated at both lateraledges that exert pressure on the web with different forces. In this way,a lateral shifting of the web can be corrected.

In U.S. Pat. No. 5,323,944, a device for controlling the lateralposition of a web is described with which the web is guided between apressure roll and a counter-pressure roll. The pressure roll can bepivoted, and the force exerted on the counter-pressure roll along itsshaft or axle can be varied in order to shift the side edges of the web.The current position of the side edges of the web is acquired usingoptoelectronic sensors.

U.S. Pat. No. 6,104,907 describes a device for guiding a paper web in aprinter. In order to avoid vibrations and variations in speed, the webis guided around rolls and is clamped by them, which also counteracts alateral shifting of the web. For example, in order to avoid lateralshifting, a guide roll is used having pins that engage in correspondingholes in the web. In another variation, the force that a roll exertsalong its axis on the web is varied. In another variation, the web isguided between pairs of upper and lower rolls. These upper and lowerrolls wrap and clamp the web with an enlarged wrap angle, thuspreventing a variation in speed of the web.

From documents DE 689 07 466 T2, DE-OS 14 24 318, DE 195 20 637, and DE199 60 649 A1, web guiding devices are known for guiding an endless web.In addition, pivotable draw-off devices for paper webs are known from DE199 53 353 A1 and DE 44 35 077 A1.

SUMMARY

An object is to indicate devices and methods that enable a preciseguiding of an endless web, and with which a sagging at one side of theweb is avoided.

In a method or device for guiding an endless web, the endless web isguided via a first positionable roll to an additional positionable rollwith a predetermined angle of wrap on each roll, shafts of the rollslying parallel to one another in a plane and being held by a frame. Theweb is fed to and led away from the positionable rolls via a respectivefirst stationary roll and a respective additional stationary roll. Theframe is pivoted relative to the stationary rolls about a first axis ofrotation substantially perpendicular to the plane in order to modify aposition of an edge of the web in a direction of the positionable rollshafts. The frame is pivoted relative to the stationary rolls about asecond axis of rotation one component of which runs parallel to amovement direction of the web between the positionable rolls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are respectively side and plan views as schematicrepresentations of the paper transport device in a high-performanceprinter, having a rotating frame that can be moved in two axes ofrotation and a pivotable draw-off device;

FIG. 2 shows the design of the rotating frame;

FIG. 3 shows an inlet roll with web tension measurement;

FIG. 4 shows a schematic representation of the controlling of the webtransport device according to a first variation;

FIG. 5 shows a second variation of a control system;

FIG. 6 schematically shows a control system according to a thirdvariation;

FIG. 7 shows the design of an electrographic printer in which a webguiding system is realized;

FIG. 8 shows a schematic arrangement having a first sensor for acquiringthe side edge of the web;

FIG. 9 shows a block diagram of the control circuit for controlling theposition of the side edges;

FIG. 10 shows a schematic design with an additional second sensor in thefeed-in area of the web;

FIG. 11 shows a block diagram of the position control system having twosensors;

FIG. 12 shows the design with three sensors;

FIG. 13 shows the block diagram of the position control system in whichthe signals of the three sensors are taken into account;

FIG. 14 shows a rotating frame having a single driven roll andcounter-pressure rolls;

FIG. 15 shows a schematic view according to FIG. 1 in cross-section;

FIG. 16 shows an example with a small wrap angle;

FIG. 17 shows examples in which the axis of rotation of the frame standsperpendicular to the drawn-off web;

FIG. 18 shows examples in which the axis of rotation runs parallel tothe direction of movement of the drawn-off web;

FIG. 19 shows an example of a web guiding device;

FIG. 20 shows an example of a web with attached adhesive labels;

FIG. 21 shows the roll characteristic of the counter-roll having a softlining or facing;

FIG. 22 shows a roll having labels that are glued to the side of thedriven roll;

FIG. 23 shows an arrangement in which the counter-roll device is pivotedaway; and

FIG. 24 shows a web guiding device having a stationary driven roll and amultiplicity of counter-rolls that can be rotated.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the preferred embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and/or method, and suchfurther applications of the principles of the invention as illustratedtherein being contemplated as would normally occur now or in the futureto one skilled in the art to which the invention relates.

According to this solution, the endless web is guided via two rolls witha predetermined wrap angle for each roll. The shafts of the rolls aresituated parallel to one another in a plane and are held by a frame. Theframe can be pivoted about a first axis of rotation essentiallyperpendicular to this plane in order to modify the position of the edgeof the web in the direction of the roll shafts. In this way, a lateralshifting of the web can be corrected. In addition, the frame can bepivoted in a second axis of rotation having one directional component inthree-dimensional space that runs parallel to the direction of movementof the web between the two rolls. In this way, the web tension can bemodified on one side of the web, so that a sagging of the web at oneside is avoided. The second axis of rotation can also run exclusivelyparallel to the direction of movement of the web. The additionalcomponents in three-dimensional space then relate to the zero directionof movement. However, constructive advantages result from an obliquepositioning of the axis of rotation in relation to the direction ofmovement, where only one component need run parallel to the citeddirection of movement.

According to a further aspect of the preferred embodiment, a method isindicated for guiding an endless web.

FIGS. 1A, 1B schematically shows the transport of an endless paper web10 through a high-performance printer. In the upper half FIG. 1A, a sideview is schematically shown, and in the lower half of the Figure a topview is shown. The web transport through the printer takes place inthree zones Z1, Z2, and Z3. In zone Z1, paper web 10 is conveyed througha pull-back device 12 that contains a roll 14 and a counter-pressureroll 16. Pull-back device 12 is used to give paper web 10 apredetermined tension in the direction of transport. Paper web 10 issubsequently deflected at a deflector roll 18 and is supplied to aninlet roll 20 that is positioned before a rotating frame 22, as seen inthe direction of transport. Inlet roll 20 comprises two sensors S1, S2for measuring the tensile force on the web, as is explained in moredetail below. Rotating frame 22 contains two positionable rolls 24, 26whose shafts are parallel to one another and are held by a frame 28shown in broken lines. Frame 28 can be pivoted about an axis of rotation30 in the direction of arrow 32. The web transport system is monitoredby two sensors S3, S4 that monitor paper web 10 from above in the areabetween positionable rolls 24, 26. Alternatively, the web 10 can also bemonitored from below using corresponding sensors.

In the output area of rotating frame 22 an edge sensor 34 is situatedfixedly on the device that determines the actual position of the sideedge of paper web 10. Dependent on the actual position and the deviationof the edge from a target position, rotating frame 22 is pivoted on aframework about axis 30, so that the side edge is controlled to apredetermined target position.

As seen in the direction of transport of paper web 10 after rotatingframe 22 in zone Z2, there is situated a stabilizing roll 36 that actsto compensate the tension in paper web 10. Stabilizing roll 36 can beslightly flexible or yielding radially, thus effecting a passivecompensation for web 10. In addition, a deflecting roll 38 and a driveroll 40 are situated in this zone Z2. Drive roll 40 exerts a tensileforce on paper web 10 and transports web 10 forwards against theresistance of a braking device 13, e.g. a vacuum brake. Drive roll 40determines the speed with which paper web 10 is transported forwards.Alternatively, pullback device 12 can be used as a permanent brake.

In zone Z3, paper web 10 is printed on one or both sides at transferrolls 42, 44. Web 10 subsequently passes through a fixing station 46 inwhich the toner images applied to web 10 are fixed, for example byinfrared fixing. In the area of fixing station 46 there are situatedsensors S5, S6 that monitor paper web 10. At the end of zone Z3 there issituated a draw-off device 48 having rolls 49, 50 that draw off web 10with a predetermined tensile force.

In the case of limited infrared fixing, paper web 10 must not come intocontact with mechanical parts between draw-off device 48 and transferrolls 42, 44, in order to avoid smudging of the toner image. Sagging atone side of the paper web must therefore be stopped.

Draw-off device 48 can be pivoted in the direction of double arrow 56about an axis of rotation 54 that passes through rotation point 52. Inthis way, the tension can be varied along the two side edges 11, 13 ofpaper web 10, in order to reduce or to prevent a sagging at one side ofpaper web 10.

Rotating frame 22 can additionally be pivoted in a second axis ofrotation 58 in the direction of arrow 60. Axis 58 runs essentiallyparallel to or identical to the direction of movement of paper web 10between the two positionable rolls 24, 26. In this way, the tension onone side of paper web 10 can be increased or decreased, thus avoiding asagging comprising movement in a direction perpendicular to a plane ofthe web at one side of paper web 10.

In the lower part FIG. 1B, a top view of the transport of paper web 10through the high-performance printer is shown. In a variation, thetransport of paper web 10 takes place in such a way that one side edgehas a fixed target position independent of the width of paper web 10. Inthe present example, this has been determined to be the left side edge11, seen in the direction of transport. This side edge 11 agrees withsecond axis of rotation 58. In the present example according to FIG. 1,a pivoting of the entire rotating frame 22 takes place about axis ofrotation 58 by pivoting frame 28 about a bearing 62 that is situatedapproximately below the prolongation of axis of rotation 58. For thispurpose, a screw-nut combination 64 is situated on the opposite side ofbearing 62, with which frame 28 can be pivoted about axis of rotation58. It is to be noted that other determinations of side edge 11 inrelation to axis of rotation 58 can be made. Other devices can also beused for the pivoting that operate electrically, hydraulically, orpneumatically. The depicted screw-nut combination 64 merely indicates aparticularly simple device that can be actuated by hand.

Sensors S1, S2 are preferably formed as force sensors, and measure theforces exerted by paper web 10 on the shaft of inlet roll 20. If theforce on one side of web 10 is reduced, the typical result is a saggingof web 10 at this side. A sagging at one side of this sort can becompensated by adjusting screw-nut combination 64.

In the one-sided determination of side edge 11 of web 10 shown in FIGS.1A, 1B, web 10 is not situated centrically in relation to inlet roll 20.This asymmetry also has the result that, due to different lever arms,asymmetrical forces occur in sensors S1, S2 along the shaft of inletroll 20. Here, the target values for a correction that may be requiredare likewise asymmetrical. They are determined for example usingcomputer programs or by measurements, and form the basis for correctivedata.

Sensors S3, S4 and S5, S6 monitor the edge areas of web 10 having sideedges 11, 13, and can recognize a sagging at one side. For example,video cameras can be used as sensors. Another possibility is to acquirethe web tension in the area of side edges 11, 13, for example using oneor more force sensors. Another possibility is to determine the saggingof the respective side edge 11, 13 using path sensors that operateoptically, inductively, and/or capacitively.

FIG. 2 schematically shows rotating frame 22 having two rolls 24, 26,whose shafts 66 run parallel to one another and are held by frame 28.Through a rotation in the direction of arrow 32 about axis 30 inrelation to stationary rolls W1, W2 (inlet roll 20 and stabilizing roll36 in FIGS. 1A, 1B), the position of side edges 11, 13 of web 10 can bemodified in the direction of roll shafts 66. Through a pivoting in thedirection of arrow 60 about axis 58, the tension within paper web 10 canbe modified at the side of an edge 11, 13 of the web. In the exampleaccording to FIG. 2, axis of rotation 58 is situated in the center ofweb 10. However, it can also be situated at the edge of web 10, as inthe example according to FIGS. 1A, 1B, or even outside paper web 10.

FIG. 3 shows an example of the measurement of the tension of paper web10 using draw-in roll 20 and sensors S1 and S2, which are realized asbending beams with expansion measurement strips for force measurement.Inlet roll 20 is held at both ends in receptacles 68. These receptacles68 are connected fixedly with the printer housing (not shown) by meansof mounts (bending beams) 70, 72. The expansion measurement strips ofsensors S1, S2 measure the bending of these mounts 70, 72, and thus theforces F1, F2 that occur at each side of draw-in roll 20, which, givenan asymmetrical situation of paper web 10 and draw-in rolls 20, areapproximately proportional to the tension in each side edge 11, 13 ofpaper web 10. Sensors S1, S2 provide electrical signals via lines 74,76. If the web tension in the area of a side edge 11, 13 of web 10 isless than the target value, the respective force F1, F2 is also lessthan the target value, so that a sagging of this side edge 11, 13 of web10 can be inferred. Given an asymmetrical situation of paper web 10 anddraw-in roll 20, the lever arms for sensors S1, S2 along the shaft ofinlet roll 20 are to be taken into account, i.e., the target forces arelikewise asymmetrical and the forces are to be corrected accordingly.

The depicted measurement of the tension of paper web 10 at draw-in roll20 can of course also be applied at other rolls in the web transportthrough the printer, so that using a similar system it is possible todetermine sagging at one side of web 10 at almost any location withinthe printer.

FIGS. 4, 5 and 6 show three variations for controlling or regulating theweb tension in the printer. In the variation according to FIG. 4, acontrolling or regulating of the web tension takes place using sensorsS3, S4 on rotating frame 22 as well as sensors S5, S6 in the area offixing station 46. The signals of sensors S3, S4 and S5, S6 are providedto a control unit 80 that processes them preferably by means ofsoftware, in a control or regulation algorithm. This control unit 80then produces control signals 82, 84 for controlling correspondingdrives for rotating frame 22 and for draw-off device 48. The controlalgorithm processes predetermined target values 86; control unit 80 alsoproduces items of information concerning operating states that are shownon display 88.

If it has been determined with the aid of sensors S3, S4 that in thearea of rotating frame 22 web 10 is sagging along a side edge 11, 13,rotating frame 22 is pivoted about axis of rotation 58, for exampleusing an electrically actuated screw-nut combination 64 or using otherpivot mechanisms. In this way, paper web 10 is made rigid in the saggingarea. In a similar manner, a sagging at one side in the area of fixingstation 46 is acquired by sensors S5, S6 and is counteracted and/orcompletely compensated by pivoting draw-off device 48 about axis ofrotation 52 along double arrow 56. In this way, a sagging at one side isalso corrected in the area of the fixing. In the described firstvariation, a sagging at one side in the area of rotating frame 22, aswell as in the area of fixing station 46, is thus corrected. This cantake place using control algorithms that are stored in the control unit.However, a regulating can also take place in such a way that targetvalues are pre-indicated to the control unit and are compared withactual values from sensors S5, S6 and S3, S4; any deviation is correctedby adjusting rotating frame 22 or draw-off device 48.

In the second variation according to FIG. 5, in which identical partshave identical reference characters, for the correction of the webtension the signals of sensors S1, S2 in the area of draw-in roll 20 andsensors S5, S6 in the area of fixing station 46 are evaluated. With theaid of the signals from sensors S1, S2, a web tension that is lessenedalong one edge 11, 13 of paper web 10 can be detected, which isinterpreted as a sagging at one side of paper web 10. Rotating frame 22is then controlled so as to counteract this decreasing of the tension atthis side of web 10. By means of a control algorithm, the pivoting ofrotating frame 22 about axis of rotation 58 takes place in such a waythat predetermined forces are achieved for sensors S1, S2. The settingof the web tension with the aid of sensors S5, S6 takes place asdescribed in relation to the variation according to FIG. 4. In thisvariation as well, a sagging of the paper web at one side is correctedor avoided in the area of rotating frame 22 and in the area of fixingstation 46.

In the variation according to FIG. 6, a monitoring of paper web 10 takesplace only with the aid of sensors S1, S2, which are situated in thearea of draw-in roll 20. Assuming that the axes of all the conveyorrolls for transporting the paper web are in a basic setting in whichthey are parallel to one another, a sagging at one side of paper web 10can be caused only by non-uniform mechanical characteristics of paperweb 10. The signals from sensors S1, S2 thus provide diagnosticinformation about the characteristics of the web, for example as towhether the web is curved, or has a varying density, or has varyingtensions along the axes of its surface. With the aid of empirical valuesdetermined from trials and measurements, for each tuple of values ofsensors S1, S2, in which the web width and type of paper are also takeninto account, an associated deflection of rotating frame 22 about axis58 and/or an associated deflection of draw-out device 48 about axis ofrotation 52 can take place. Typically, such tuples of values, and theassociated control parameters for the required deflection for therotating frame and for draw-off device 48, are stored in a memory as atable. In this variation, the expense for sensors is minimal, but ahigh-quality guiding of the paper web in the printer is achievednonetheless. Of course, the described variation according to FIG. 6 canalso be combined with the variations according to FIG. 4 or FIG. 5,i.e., the signals of sensors S3, S4 and/or S5, S6 can also be used forthe controlling and regulation of paper web 10.

According to a fourth variation, a monitoring of the web tension and acorrection take place only in the area of fixing station 46, in order toavoid a harmful sagging at one side of the paper web. With the aid ofthe signals from sensors S5, S6 and pivotable draw-off device 48, astable web guiding is achieved for the relatively long path of a fixingstation 46 operated with infrared radiation.

In FIGS. 7 to 13, according to a further aspect of the preferredembodiment examples are described that can also be combined with theexamples described above. FIG. 7 shows a high-performance printer inwhich the device and method according to the preferred embodiment arerealized. The printer is divided into a printing mechanism 110 and afixing station 112, each having an independent housing 114, 116 that areconnected to one another. A web 118 of endless paper is fed through bothhousings 114, 116. In a web inlet area 120 for printing mechanism 110there is situated a web pull-back motor 122 that exerts a retainingforce on web 118 with the aid of a pair of rolls. In addition, a webbrake 124 is provided that smoothes web 118 and likewise exerts aretaining force on web 118. Web brake 124 is, for example, realized by apiece of felt that lies against web 118. Another possibility is to use avacuum brake. Here, a variable vacuum is used to apply a vacuum, i.e.suction, to the underside of the web, and the frictional force ismodified accordingly. In the web inlet area of pull-back device 120, or,more precisely, just after (seen in the normal direction of transport)web brake 124, a second sensor 126 is situated that acquires the actualposition of the side edge of web 118.

Via a deflecting roll 128, web 118 is supplied to a rotating frame 130that acts as an actuating element for shifting the position of the sideedge of web 118. Rotating frame 130 executes rotational movements aboutan axis situated perpendicular to web 118, thereby shifting the sideedge in a direction perpendicular to the plane of the paper in FIG. 7.In the outlet area of rotating frame 130 there is situated a firstsensor 132 that acquires the actual position of the side edge of web118. Via two additional deflecting rolls 134, 136, web 118 is suppliedto a web drive 138 that contains a roll pair. Web drive 138 moves web118 forward in the direction of transport, against the retaining forceof web brake 124.

Further along the transport path, an upper transfer print station 140and a lower transfer print station 142 are situated at both sides of web118. Both transfer print stations 140, 142 print toner imagessimultaneously on the upper and lower sides of web 118. The two transferprint stations 140, 142 are essentially identical in construction; forthis reason, only upper transfer print station 140 is explained in moredetail below. Upper transfer print station 140 comprises a charactergenerator 144 that produces an electrostatic charge image on aphotoconductor belt 146, corresponding to a print image that is to beprinted. An upper developer station 148 colors in the electrostaticcharge image with toner material; the toner images are then transferredonto a transfer belt 150. Further along, the toner images situated ontransfer belt 150 are then transferred onto web 118 at transfer point152; that is, at transfer point 152 toner images are transferredsimultaneously by both transfer print stations 140, 142.

Seen in the direction of transport, after transfer point 152 there issituated a third sensor 154 that also acquires the actual position ofthe side edge of web 118. The not-yet-fixed toner images on web 118 aresupplied to fixing station 112, where they are fixed and cooled on bothsides of the web in infrared fixing devices 156, 158 and subsequent fans160, 162. In the outlet area of fixing station 112 there is situated aweb draw-off motor 164 that acts on a pair of rotating rolls and thatconveys web 118 out of fixing station 112.

The depicted high-performance printer has various operating states inwhich different tasks occur that relate to controlling the position ofthe side edges of web 118:

Operating State 1: Automatic Web Placement or Insertion

When a new web 118 is put into place, with the aid of a clamp it isautomatically passed through printing mechanism 110 and through fixingstation 112, and from there is transported to the web outlet. During theguiding of web 118 with the aid of the clamp, rotating frame 130 and theposition controlling system remain inactive. After the putting intoplace of the web has been completed, rotating frame 130 and the positioncontrolling system are activated.

Operating State 2: Placement of a Glued-on Web

If a new web is glued onto a previous web, the new web is guided throughprinting mechanism 110 and fixing station 112 with a transport speedthat is significantly less than the normal print speed, in order not tooverload the glued point. During the transport of the glued pointthrough the printer, a controlling adapted to the slow transport speedis active. Positional deviations at the side edge can occur as a resultof the glued point between the old web and the new web. The controllingtask here is to cause the side edge of web 118 to settle into a targetposition as quickly as possible. After the web has been put into place,the normal positional controlling is activated.

Operating State 3: Slow Forward Transport and Backward Transport of theWeb

In order to position the web as precisely as possible when pre-printedpaper (form paper) is being put into place, a slow forward and backwardtransporting is required. During this positioning, the control deviceand rotating frame 130 are not active. After this fine positioning isterminated, the following movement of the paper activates thecontrolling and the rotating frame 130, and the side edge of web 118should be brought into the target position as quickly as possible (as inoperating states 4 and 5 described below). In this process, it isimportant that there be as few wasted sheets as possible.

Operating State 4: Rapid Forward Transport Without Print Operation

At the end of a print job, the side edge of the web should be held inthe target position with a defined printing speed, but without printingoperation, so that the last-transferred toner images can be fixed infixing station 112. At the end of the forward motion of web 118, abackward motion is introduced so that a new beginning of the operationcan be carried out in a correct relation to the form; that is, the printimages must be printed on web 118 with a precise positioning in relationto a form. During this forward and backward movement of the web, thecontrolling and the rotating frame 130 are active; the target positionof the side edge of the web should be achieved as quickly as possible,resulting in only a few wasted pages.

Operating State 5: Web Transport in Print Operation

At the start of the print operation, web 118 is first brought to thetarget speed, corresponding to the print speed, with transfer stations140, 142 pivoted away. The transfer stations with the transfer belts aresubsequently pivoted into place and print operation takes place. At theend of a print operation with forward movement of the web, a backwardtransport of web 118 is carried out with pivoted-away transfer stations,so that a new beginning of the print operation can take place with acorrect positioning in relation to the form. In this operating state thecontrolling and the rotating frame 130 are active. A rapid settling ofthe side edge into the target position should take place within thevarious transport speeds of web 118.

On the basis of a first example having only one sensor 132, FIG. 8schematically shows the path of web 118 inside devices 110, 112 that isnecessary for controlling the position of the side edge. Web 118 isconveyed through web inlet area 120, symbolized by a pair of rolls, torotating frame 130, in whose web outlet first sensor 132 is situated.Web 118 is subsequently guided along web drive 138, transfer point 152,and draw-off device 164.

FIG. 9 shows a block diagram of the position controlling system for thefirst exemplary embodiment. Actual signal S1 from first sensor 132 issupplied to an adder element 170, and control deviation E is formed. Acontroller 172, for example a PID controller, produces a control signalR that is supplied to rotating frame 130 as actuating element 130. Onthe basis of control signal R, rotating frame 130 modifies its angle ofrotation, thus modifying the lateral position of the side edge of web118. The actual position of the side edge is acquired by first sensor132 as actual signal S1, which, as mentioned, is fed back to adderelement 170. This control process continues to take place until controldeviation E is equal to zero. The target position and target signal S0are defined at the location of first sensor 132 as an electrical signal.

First sensor 132 determines measurement values at predeterminedintervals along the path of web 118. A mean value of these measurementvalues is used as actual signal S1. Preferably, a sliding mean value oran exponential mean value is used as the mean value. In the case of asliding mean value, first a mean value is formed from n measurementvalues. For each new measurement value that is added, a new mean valueis calculated from the previous mean value and the new measurementvalue. Target value S0 can be determined in a similar manner in acalibration process. Preferably, the mean value is determined over apredetermined length of the web, in general a whole-number multiple of astandard format length of a print page. Typically, the 12-inch format isused as a standard format length, and the multiple factor is preferably3.

Due to the mean value formation, short-waved positional deviations alongthe edge of the web do not result in undesirable deflections of therotating frame. Moreover, due to the mean value formation, excessivepositional deviations, caused by resonance, at the transfer printingpoint are avoided. Such positional deviations caused by resonance canoccur in paper webs having side edges cut in the form of waves. Due tothe calibration to the standard format length, waviness does not occuralong printed lines in print images in the direction of transport of theweb within a form length.

In this first exemplary embodiment, it can be problematic that theactual position agrees with the target position of the side edge only atthe location of first sensor 132, i.e., in the vicinity of rotatingframe 130. At transfer point 152, which is essential for the printquality, the side edge of web 118 can again deviate from a targetposition. As a result of the mean value formation, moreover, thesettling-in or response characteristic can be relatively slow. Inaddition, due to the mean value formation a control deviation can remainpermanently, because maximum amplitudes are not removed by thecontrolling.

FIG. 10 shows a further exemplary embodiment having two sensors.Identical parts are designated with identical reference characters.Second sensor 126 is situated in web draw-in area 120. The rest of thesystem agrees with the one shown in FIG. 8.

FIG. 11 shows a block diagram of the associated position control systemfor the side edge of web 118. With the aid of signal S2 from secondsensor 126, controller 172, which outputs control quantity R to rotatingframe 130, is influenced. Second sensor 126 represents, in its signalS2, the deviation of the position of the side edge of web 118 in webdraw-in area 120, i.e., it determines the deviation of the actualposition of the side edge from a target position in the area of webbrake 124 (cf. FIG. 7). For this purpose, it is useful that in webdraw-in area 120 there is situated a web feed-in device that comprises alateral stop (not shown) along which the relevant side edge of web 118is guided. In this way, a stable initial situation for the side edge ofthe web is created in the draw-in area of web 118.

Second sensor 126 preferably contains a delay element VZ. The delay timefor signal S2 corresponds to the time required for web 118 to betransported from the location of second sensor 126 to the location offirst sensor 132. In this way, the deviation of the side edge from atarget value in web draw-in area 120 can be compensated in atime-delayed manner. Thus, the deviation of the side edge from areference value in the web draw-in area is determined, and as a firstalternative, signal S2 is added to target value S0 (shown in brokenlines in FIG. 11). As a second alternative, signal S2 is applieddirectly to controller 172, which forms control quantity R, taking intoaccount this signal S2. In this exemplary embodiment according to FIG.11, no mean value formation is carried out for signal S1 of first sensor132, because this would disturb the compensation using signal S2.

The advantage of the positional controlling according to FIG. 11 is thatonly the long-waved deviations of the mean actual position of the sideedge from a target position at the location of first sensor 132 arecompensated by rotating frame 130. Due to the taking into account of adeviation of the side edge in the draw-in area of web 118, the startupor response characteristic of the control circuit is relatively fast. Inthis example according to FIG. 11, it is also to be noted that thecontrol deviation at the location of first sensor 132 can be minimal,but at the location of transfer point 152 deviations from an optimalposition of the side edge can nonetheless occur.

FIG. 12 schematically shows the design having three sensors 126, 132,and 154. Second sensor 126 is optional, as is indicated by broken lines.Third sensor 154 is situated within an area of ±100 mm relative totransfer point 152 of transfer stations 140, 142, because transfer point152 itself is difficult to access.

FIG. 13 shows the associated positional controlling using signals S1 ofthe first sensor, S3 of the third sensor, and, optionally, signal S2 ofthe second sensor. The positional control system contains, in additionto addition element 170, addition elements 174 and 176. Addition element176 is supplied with signal SU, which reproduces the target position atsensor 154, i.e., in the vicinity of transfer point 152. Additionelement 176 carries out the target value/actual value comparison betweensignals SU and S3. The result is supplied to addition element 174, whoseresult is in turn supplied to addition element 170. At addition element170, actual value S1 of first sensor 132 in the area of rotating frame130 is taken into account. As in the example according to FIG. 5, thesignal of second sensor S2 can optionally be taken into account as adelayed signal at controller 172 or at addition element 170 (thisvariant is not depicted). Optionally, signal S2 can also be taken intoaccount in the formation of signal S3, i.e., signal S2 acts on thirdsensor 154.

With the aid of the controlling according to FIG. 13, it is possible totake into account the positional deviation directly at transfer point152. Signal S3, possibly also taking into account signal S2, forms,after combination in adder elements 176 and 174, target signal S0 forthe control circuit containing addition element 170. In order to keepthe control system free of oscillations, signal S0 must change onlyslowly, for example more slowly than signal S1 by a factor of 110. Theadvantage of the arrangement according to FIG. 13 is that a deviation ofthe side edge in the area of transfer point 152 is also recognized andis controlled out by rotating frame 130.

In the following FIGS. 14 to 24, examples of a rotating frame are shownaccording to a further aspect of the present invention. These examplescan be combined with the previously described examples. In FIG. 14, aweb guiding device is shown that has a single driven roll 210 mounted ina rotating frame 212. Rotating frame 212 can be pivoted about an axis ofrotation 214 that runs essentially perpendicular to drawn-off web 216.Within rotating frame 212, counter-rolls 218 are also mounted that pressweb 216 against roll 210 with a predetermined force. Roll 210 is drivenby a drive 220 and a gear mechanism 222. Due to the friction on thesurface of roll 210, web 216 is conveyed in the direction of arrow P21.Web 216 has the tendency to be conveyed in the tangential direction awayfrom the surface of the jacket of roll 210. By rotating the rotatingframe 212 by an angle α about axis 214 corresponding to arrow P22, thetransport direction of web 216 conveyed by roll 210 is also influenced.Accordingly, the position of the edge of web 216 in relation to areference position can be modified in the direction of the shaft of roll210.

In order to rotate rotating frame 212, an electrical drive 226 can forexample be used that moves rotating frame 212 by small angular amounts,typically by 1°, clockwise or counterclockwise corresponding to arrowP22. Drive 226 contains a nut 228 in which a spindle 230 is moved backand forth. In order to ensure definite positions in the deflection ofrotating frame 212, the unavoidable play due to tolerances between nut228 and spindle 230 is prevented by a tension spring 232. This has theeffect that when spindle 230 moves forward and backward, nut 228 alwayslies against the same flank of the spindle.

When there is a rotational movement in the direction of arrow P22,conveyed web 216 is subjected only to minimal forces. However, it isalso possible to situate axis of rotation 214 off-center in relation torotating frame 212. In the example according to FIG. 14, web 216 isguided centrically in relation to roll 210. However, it is also possibleto situate web 216 off-center.

In addition, in the example according to FIG. 14, web 216 is narrowerthan roll 210. However, it is also possible for this web to extend pastone or both sides of roll 210, so that the width of roll 210 is smallerthan the width of web 216.

FIG. 15 schematically shows the arrangement according to FIG. 14 incross-section. Web 216 comes into contact with the surface of roll 210with a predetermined wrap angle β. Typically, the angular range for thewrap angle is between 3° and 80°. The greater the wrap angle, thestronger the frictional connection is with the surface of driven roll210.

Wrap angle β defines the length of contact zone 234 in which web 216makes contact with the surface of roll 210. This contact zone 234 has asmoothing effect on incoming web 216, so that the effect of the creasingof web 216 when roll 210 is rotated is reduced. The smoothing effect canbe increased if the contact point of counter-roll 218 with web 216, seenin the direction of travel of web 216, is situated at the end of wrapangle β.

Roll 210 has on its surface a friction lining made for example of a pureclosed cell material having a hardness of approximately 80 ShA.Spring-loaded counter-rolls 218 effect a largely drag-free transmissionfrom driven roll 210 to web 216. Through a defined setting of thepressure forces of counter-rolls 218 on driven roll 210, a denting ordamaging of the surface of roll 210 is avoided, and a constant surfacespeed of web 216 is thus ensured. Counter-rolls 218 have a lining madeof a softer material than roll 210. For example, the lining is made offoamed pure material having a hardness of approximately 50 ShA.

FIG. 16 shows an example having a small wrap angle β. With a wrap angleof this sort as well, the position of web 216 can be shifted by rotatingthe rotating frame.

FIG. 17 shows an example in which web 216 is fed in from below. Inaddition, axis of rotation 214 is situated perpendicular to drawn-offweb 216, as can be seen in examples a) and b). Examples c), d), and e)show web guiding in a top view in example a), with various angles ofrotation α in relation to a normal position of 0°.

FIG. 18 shows an example in which axis of rotation 214 is situatedparallel to the direction of transport of drawn-off web 216. When thereis a rotation by angle of rotation P12, a change of the position of web216 likewise takes place in the direction of shaft 224 of roll 210.Examples a) and b) illustrate the arrangement with axis of rotation 214situated parallel to the direction of transport of web 216. Examples c),d), and e) show different deflections in the direction of angle ofrotation P22, seen in the direction of axis of rotation 214.

FIG. 19 shows a web guiding device 240 that is situated before thedriven roll 210 depicted in the preceding Figures, seen in direction P10of web transport. Web guiding device 240 acts on the one hand to preseta position of the edge of web 216, and on the other hand to create apredetermined web tension.

Web guiding device 240 contains a guide sheet 242, for example a guideplate, in the form of a partial cylinder jacket surface on which web 216slides. Guide sheet 242 has, at each web edge side, plates 244, 246 thatguide web 216 at both sides. The spacing from one another of plates 244,246 can be adjusted to fit the width of web 216.

Before guide sheet 242, guide elements 248, 250, 252 are situated thatcan also bear plates, as is shown for guide element 252 with plates 254,256. These plates 254, 256 have the effect that web 216, drawn off by aroll 258, already assumes a predetermined lateral position in the inletarea.

Guide elements 248, 250, 252 can be realized as cylinders over whoserespective jacket surfaces web 216 is guided at predetermined wrapangles. The respective wrap angle can be set by modifying the positionof the shafts of guide elements 248, 250, 252 relative to one another.This is important if the same web tension is required for web materialshaving different thicknesses.

In order to further set the web tension in a defined manner, a brakingdevice is provided that engages guide sheet 242. For example, thisbraking device can be realized by a felt flap 260 that presses with amodifiable weight against web 216 sliding over guide sheet 242. Inaddition, devices as described in patent application DE 44 01 906 of thepresent applicant can be used for the pre-centering and tightening ofweb 216. The cited patent application DE 44 01 906 is herebyincorporated by reference into the content of the disclosure of thepresent application.

FIG. 20 shows a web 216 provided with adhesive labels E. In a web 216 ofthis sort used in practice, in a printer or copier only the labels areto be printed. Here the problem arises that when the edge of a labelmeets counter-roll 218, this counter-roll is deflected by a traveldistance h, as is shown in broken lines in FIG. 19. The travel work ofcounter-roll 218 that is applied causes an abrupt change in torque, withan accompanying change in the load angle on drive motor 220 (cf. FIG.14). During operation, in a printer such an effect results in aworsening of the print image, in particular if fine gray rasters areprinted. The use of a soft lining for counter-pressure roll 218, forexample a foamed pure material, reduces this effect, because the travelenergy of counter-roll 218 is absorbed by the elasticity of the lining.

In FIG. 21, it is indicated that the travel h is reduced if acorresponding elastic lining is used.

FIG. 22 shows an arrangement of web 216 in which the labels are situatedon the side facing driven roll 210. Due to the wedge effect of web 216on the edge of the labels, a kind of starting bevel is formed, so thatthe travel work for counter-roll 218 is not applied abruptly. Of course,the arrangement according to FIG. 22 can be combined with thearrangement according to FIG. 21.

FIG. 23 illustrates that counter-rolls 218 can be jointly pivoted awayfrom driven roll 210, thus opening a gap SP that is sufficiently largeto admit a web 216, shown in broken lines. In this way, the putting intoplace of a new web 216 is made easier.

FIG. 24 shows a further example of the preferred embodiment. Driven roll210 is situated in stationary fashion, i.e., its axis does not change.Counter-roll device 270 contains a multiplicity of rolls 272 that pressweb 216 against roll 210. The multiplicity of rolls 272 and roll 210 areheld by a rotating frame. Each roll 272 can be pivoted to the samedegree about an axis of rotation 274. Through a rod 276 that engageswith a lever end for each roll 272, the angle of rotation of therespective roll 272 can be adjusted. Here as well, web 216 has thetendency to be conveyed away in a direction tangential to the surface ofthe respective roll 272, and in this way the position of the edge of web216 can be modified in the direction of the roll shaft. The additionalvariations described above, for example with respect to the linings ofdriven roll 210 and the linings of rolls 272, can also be used here.

Many variations are possible. The rotating frame described in FIG. 14can for example be part of a control circuit. The actual position of theedge of web 216 is determined with the aid of a sensor in relation to atarget position. Dependent on the signal from the sensor, the angle ofrotation P12 of the frame is adjusted in steps or continuously in such away that a control deviation between the actual position and the targetposition of the edge is reduced.

In relation to the exemplary embodiment according to FIG. 24, allcounter-pressure rolls 272 are controlled simultaneously with the aid ofrod 276 and a drive. This drive can be part of a control circuit. Withthe aid of a sensor, the actual position of the edge in relation to atarget position is determined. Depending on the signal of the sensor,the angle of rotation for each counter-roll 272 is adjusted in such away that a control deviation between the actual position and the targetposition of the edge is reduced or eliminated.

The depicted examples of the various aspects of the preferred embodimentcan be advantageously combined with one another, resulting in furthervariations. Thus, the rotating frame shown in FIGS. 14 and 24 can beused in the example according to FIGS. 1 and 7. The controlling of theside edge of the web according to FIGS. 7 to 13 can be used in theexamples according to FIGS. 1 to 7 and FIGS. 14 to 24.

Although in the drawings, and in the above description, a preferredexemplary embodiment has been shown and described in detail, theseshould be understood only as examples, and not as limiting the presentinvention. It is hereby noted that only the preferred exemplaryembodiment has embodiments have been represented and described, and thatall changes and modifications lying within the scope of protection ofthe present invention currently and in the future are to be protected.

1. A device for guiding an endless web, comprising: a first positionableroll which guides the endless web directly to an additional positionableroll with a predetermined wrap angle on each positionable roll, shaftsof said positionable rolls lying parallel to one another in a plane andbeing held by a frame; the web being fed to and led away from thepositionable rolls via a respective first stationary roll and arespective additional stationary roll; the frame being pivotablerelative to the stationary rolls about a first axis of rotation which issubstantially perpendicular to said plane in order to modify a positionof an edge of the web; the frame being pivotable relative to thestationary rolls about a second axis of rotation parallel to a movementdirection of the web between the first and additional positionable rollswith an actuated adjustment device that is actuated by at least one ofthe functions selected from the group consisting of manually,electrically, hydraulically, and pneumatically to make said web rigid toprevent sagging; and along the web there is situated at least one sensorthat acquires a sagging comprising a movement in a directionperpendicular to a plane of the web at one side of the web and indicatesit via a control device, and in which, dependent on the indication, theframe is pivoted about the second axis of rotation.
 2. A deviceaccording to claim 1 in which an inlet roll is situated before the frameand a stabilizing roll is positioned after the frame as said stationaryrolls, and said stationary rolls feed the web in and lead it away.
 3. Adevice according to claim 1 in which a screw-nut combination is used forthe pivot.
 4. A device according to claim 1 in which a sensor issituated in a vicinity of the frame at both sides of the web.
 5. Adevice according to claim 1 in which a force sensor is used thatacquires web tension.
 6. A device according to claim 5 in which theforce sensor acquires a force that is exerted at one side at an inletroll via which the web is fed into the frame.
 7. A device according toclaim 1 in which a distribution of a tension of the web in an areabetween the two positionable rolls of the frame is acquired by sensorsas a one-sided sagging or as a wave.
 8. A device according to claim 1 inwhich, as seen in the movement direction of the web a fixing stationthat fixes a toner image is situated after a transfer station.
 9. Adevice according to claim 8 in which as seen in the movement directionof the web after the fixing station there is situated a draw-off devicefor the web that is pivotable in order to correct a one-sided sagging ofthe web.
 10. A device according to claim 8 in which web tension in anarea of the fixing station for fixing a toner image on the web isacquired by at least one sensor, and a pivoting of a draw-off devicetakes place dependent on a signal of the sensor.
 11. A device accordingto claim 10 in which the draw-off device contains two rolls that arepivotable about an axis of rotation.
 12. A device according to claim 11in which the axis of rotation runs substantially perpendicular to theweb.
 13. A device according to claim 1 in which first sensors on thepivotable frame as well as second sensors in an area of a fixing stationmonitor the web, a control unit which pivots the pivotable frame aboutthe second axis of rotation dependent on signals from the first sensorsand the control unit pivots a draw-off device about an axis of rotationdependent on signals from the second sensors.
 14. A device accordingclaim 1 in which first sensors in an area of an inlet roll and secondsensors in an area of a fixing station monitor the web, and in which acontrol unit pivots the pivotable frame about the second axis ofrotation dependent on signals from the first sensors, and pivots adraw-off device about an axis of rotation dependent on signals from thesecond sensors.
 15. A device according to claim 1 in which only firstsensors in an area of an inlet roll acquire the web, and a control unitrotates the pivotable frame about the second axis and rotates a draw-offdevice about an axis of rotation dependent on signals from firstsensors.
 16. A device according to claim 1 in which the endless web isdesigned as a paper web without edge perforation.
 17. A device accordingto claim 1 wherein it is used in a printer or copier.
 18. A method forguiding an endless web, comprising the steps of: guiding the endless webvia a first positionable roll directly to an additional positionableroll with a predetermined angle of wrap on each roll, shafts of therolls lying parallel to one another in a plane and being held by aframe; the web being fed to an led away from the positionable rolls heldby the frame via a respective first stationary roll and a respectiveadditional stationary roll; the frame being pivotable relative to thestationary rolls about a first axis of rotation substantiallyperpendicular to the plane in order to modify a position of an edge ofthe web; the frame being pivotable relative to the stationary rollsabout a second axis of rotation parallel to a movement direction of theweb between the positionable rolls with an actuated adjustment devicethat is actuated by at least one of the functions selected from thegroup consisting of manually, electrically, hydraulically, andpneumatically to make said web rigid to prevent sagging; and positioningat least one sensor situated along the web that detects a saggingcomprising a movement in a direction perpendicular to a plane of saidweb of one side of the web, the at least one sensor producing a signaldependent on the detected sagging, said signal being supplied to acontrol circuit that pivots the frame about the second axis of rotationin such a way that the one-sided sagging of the web is reduced or iscontrolled to a value zero.
 19. A method according to claim 18 in which,as seen in a movement direction of the web, there is situated after afixing station a draw-off device for the web that pivots in order tocorrect a one-sided sagging of the web.